Method for the separation of blood plasma particles from a blood plasma suspension

ABSTRACT

Method for separating blood plasma particles from a blood plasma suspension in a self-discharging centrifuge having two or more discharge slits and axially stacked baffle plates, in which the blood plasma particles are separated from the liquid phase by centrifuging and removal of the liquid phase, suctioning off liquid remaining in the drum after separation of the blood plasma particles and discharging the sediment of solid blood plasma particles from the drum by centrifugal force into a collecting container underneath the drum, the drum and the blood plasma sediment being cooled during one or more of the process steps.

This is a 371 of PCT/EP02/08444 filed 30 Jul. 2002 (international filingdate).

The invention relates to a method for the separation of blood plasmaparticles from the liquid phase of a blood plasma suspension, such astypically obtained in the fractionation of human blood plasma.

BACKGROUND OF THE INVENTION

According to the prior art, blood plasma suspensions are presentlyseparated using vertical solid-bowl centrifuges or chamber separators orby filtration methods.

Filtration of blood plasma is carried out via filter presses orvertically arranged rotary pressure filters. The throughput capacitywhich can be achieved thereby is relatively high. However, in most casesa filter aid has to be added to the suspension, namely a porous, finelyparticulate material which increases the permeability of the filter cakeforming in the filter. This has a significant influence on the procedurefor further processing to give the end product.

When using filters for the separation of blood plasma particles, themain problem, however, lies in the complicated manual handling which isneeded for emptying the filter and cleaning it, and in the associatedrisk of contamination to which operating staff and product are equallyexposed. A further disadvantage of this method is that the filters usedaccording to the prior art cannot be cooled, and the procedure thereforehas to be carried out at relatively low ambient temperatures. Thisentails high costs associated with air conditioning.

Alternatively, the separation of blood plasma particles in chamberseparators is known. Chamber separators are characterized by a drumwhich is mounted on a vertical spindle, without automatic discharge ofthe separated solid, and which is filled from above via a vertical lineand, in order to improve the clarification effect, is in most casesdivided into a plurality of chambers. These centrifuges can be cooledvia the housing. The throughput capacity is relatively high. However,the use of chamber separators for the separation of blood plasmaparticles also has the disadvantage that the drum and other componentparts coming into contact with the product have to be removed andcleaned by hand, which exposes operating staff and product to a highrisk of contamination. Moreover, with this type of machine, no design isknown in which the drive unit is spatially separate from the processingunit, which separation is desirable in view of the increasing hygienedemands.

A more automated method for the separation of blood plasma particles ispossible using a vertical solid-bowl centrifuge with scraper device. Itis known that this type of centrifuge permits automatic discharge ofsolid and automated cleaning of the drum and of the parts coming intocontact with the product. Centrifuges of this type achieve theirseparating efficiency principally by means of very high drum speeds.However, the separating efficiency is limited because the surface areaon which the blood plasma particles are deposited is restricted forconstruction-related reasons. The high peripheral speeds which arise incentrifuges of this type require a relatively high level of cooling inorder for the drum and the product situated in the drum to be keptwithin the desired temperature range. For this reason, the spacesurrounding the drum is often placed under vacuum in order to reduce theair friction heat. The solid is discharged via a scraper system whichautomatically scrapes the deposited solid out of the drum. The solidthen falls into a container arranged underneath the drum. Because oftheir relatively complicated structure, the use of vertical solid-bowlcentrifuges with scraper system for separation of blood plasma particlesis relatively expensive, and the assembly operations are oftenlaborious.

Against the background of the known methods for the separation of bloodplasma particles, the invention aims to create the essential advantagesof said manual methods, i.e. the use of a chamber separator orfiltration, together with the essential advantages of the automatedmethod, i.e. similar to the use of a vertical solid-bowl centrifuge.Therefore, the object of the invention is to make available aninexpensive and straightforward but also fully automated centrifugingmethod with a high throughput capacity of the equipment for theseparation of blood plasma particles from a suspension, which method,however, permits cooling of the drum without the need for a vacuum inthe area of rotation of the drum and ensures separation of theprocessing space and drive space in order in particular to satisfy thestrict hygiene requirements. Assembly operations on machines used forthis method are to be able to be carried out comparatively easily.

According to the invention, this object is achieved by using anautomated centrifuge with baffle plates for increasing the activesurface area for separation of blood plasma particles from a bloodplasma suspension.

SUMMARY OF THE INVENTION

The subject matter of the invention is a method for the separation ofblood plasma particles from a blood plasma suspension in aself-discharging centrifuge, having at least an optionally coolablehousing, an admission line for the suspension, a removal line for theclarified liquid, a drum, which in particular is suspended and isconnected to a drive part lying above it and, if appropriate, isprovided with two or more discharge slits and axially stacked baffleplates, and an optionally coolable collecting container, the methodconsisting at least of the following method steps

-   (I) separating the solid blood plasma particles from the liquid    phase by centrifuging and removal of the liquid phase,-   (II) suctioning off the liquid still present in the drum after    separation of the blood plasma particles, in particular via the    admission line, the drum preferably being brought to a stop at least    for a short time, in particular for at least 5 seconds, particularly    preferably for at least 10 seconds,-   (III) discharging the sediment of solid blood plasma particles from    the drum, by centrifugal force and opening of the drum, into a    collecting container located in particular underneath the drum.

DETAILED DESCRIPTION

A method is preferred which is characterized in that the temperature ofthe drum is regulated before method step I), in particular brought to atemperature of ±5° C. in relation to the temperature of the inflowingblood plasma suspension. The temperature regulation of the drum beforemethod step I) takes place especially preferably with the drum rotating,very particularly preferably at a drum speed in the range of from 20% to70% of the drum speed used for the centrifuging in method step I).

In this connection, the drum speed can be constant throughout the periodof precooling or it can be increased in two or more steps orcontinuously.

The preliminary temperature regulation of the drum before method step I)takes place in particular by feeding a precooling liquid via theadmission line, preferably at a temperature in the range of ±5° C.relative to the inflow temperature of the blood plasma suspension.

Particularly advantageous is a chosen method in which, after thepreliminary temperature regulation of the drum before method step I),the precooling liquid is suctioned off from the drum via the admissionline.

During the suctioning, the capillary liquid located between the baffleplates can be centrifuged off in one or more intermediate centrifugingsteps, in which case the suctioning, during rotation of the drum, can becompletely interrupted, partially interrupted or not interrupted at all.

A further preferred variant of the method is one in which, during methodstep I), the liquid phase separated in the drum is taken up by a pumpdevice positioned above the baffle plates and is removed via a removalline.

To limit the temperature of the clarified liquid which is removedrelative to the temperature of the inflowing suspension, the clarifiedliquid can run off free of pressure or at a pressure restricted to thepressure drops in the conduit.

Between method steps I) and II), in an additional centrifuging phasewith the suspension delivery switched off, it is particularly preferredfor the blood plasma sediment to be further compacted at a drum speed of80% to 130% of the separation speed in step I).

In method step II), the residual liquid is particularly preferablysuctioned off in one or more intermediate centrifuging steps.

The method for the separation of blood plasma particles from a bloodplasma suspension is preferably carried out such that, in method stepIII), the blood plasma sediment is discharged by opening the dischargeslits of the drum, at a drum speed of 30% to 130% of the separationspeed in step I), preferably at the separation speed.

In a further preferred modification of the method, the blood plasmasediment discharged from the drum is collected in a flexible bag whichis fitted into the collecting container and which is held against theinner wall of the collecting container in particular by a vacuum which avacuum attachment generates between the bag and the inner wall of thecollecting container.

In this connection, the bag can also remain in the collecting container,during said method steps I) to III) and during said optional preliminaryand intermediate steps, up to a suitable degree of filling.

In a further preferred embodiment of the method, after method step III),the method steps I) to III) are immediately repeated, until thecollecting container is filled with blood plasma sediment to apredetermined degree, and the sediment is separated off for furtherprocessing.

During one or more of method steps I) to III) and one or more of theintermediate steps, the drum and the discharged blood plasma sedimentare cooled, independently of one another, by cooling the jacket of thoseparts of the centrifuge surrounding them, in particular of the housingand/or of the collecting container, by means of a liquid cooling medium,in the temperature range of +2° C. to −50° C.

A specially chosen variant of the method is characterized in that duringthe entire method, or during selected steps thereof, the drum and thesediment is cooled by feeding liquid nitrogen into the space surroundingthe drum, in particular via one or more attachments arranged on thehousing, on the baffle ring or on the collecting container, and thegaseous nitrogen is removed via an exhaust gas pipe preferablypositioned in the housing. The cooling of the drum and of the sedimentparticularly preferably takes place at least before removal of thesediment. Liquid nitrogen is preferably introduced simultaneously intothe upper area and lower area of the of the space surrounding the drum.

In a preferred variant of the method, for the purpose of checking theprocedure, the surface temperature of the drum is checked at one or morelocations during the method, in particular by a temperature-measuringdevice which is preferably arranged on the housing and conductscontactless measurement.

Centrifuges with baffle plates are typically equipped with a centralinlet for the suspension and with conical plates which are located inthe drum and which, by means of the centrifugal force present and theshort sedimentation paths and the large active separating surface area,serve as collectors for fine particles. The particles collected slidealong the plates in the direction toward the greatest diameter of thedrum and into the collection space for solids which surrounds theplates. The clarified liquid is removed on the inside of the plates bymeans of a so-called scoop designed as a pump impeller, under pressureor virtually free of pressure. Centrifuges with baffle plates are knownwhich have a standing or suspended drum. A centrifuge which is suitablein principle and can be adapted to the present method is known from DE198 46 535 A1 (corresponding to U.S. Pat. No. 6,530,871).

The method according to the invention for the separation of blood plasmaparticles is distinguished, for example compared to the use of avertical solid-bowl centrifuge, especially by the fact that thethroughput capacity of the equipment is higher, at a comparatively lowerspeed of rotation, and thus a more cost-effective method can berealized. Furthermore, on account of their simple design, preferablyused centrifuges with baffle plates involve comparatively low investmentcosts and their construction means that they are easier to assemble andmaintain. As the speeds of rotation are lower compared to the verticalsolid-bowl centrifuge, the air friction heat which develops in acentrifuge with baffle plates is relatively low. It is therefore notnecessary to operate the centrifuge under vacuum in order to maintainthe low temperatures needed for blood plasma products. The drum and theproduct can therefore simply be cooled in particular by cooling thejacket of the component parts surrounding the drum or, if necessary,cooling can be assisted by injecting liquid nitrogen into the spacesurrounding the drum.

Compared to the methods which separate blood plasma particles with theaid of chamber separators or by filtration, the method according to theinvention is distinguished especially by a significantly higher degreeof automation. Also, in contrast to methods using chamber separators andfiltration, the cleaning of the drum and of the parts coming intocontact with the product can be automated in the case of a centrifugewith baffle plates. The risk of contamination of operating staff by theproduct or of the product by soiling is therefore lower in the methodaccording to the invention. This takes account of the increased hygienerequirements, which may also possibly increase still further in future.

The method according to the invention thus combines the essentialadvantages of methods using vertical solid-bowl centrifuges, such asautomatic product discharge and automatic cleaning, with the advantagesof the methods using chamber separators or filters, such as the highthroughput capacities, simple structural components and cost-effectiveoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

The method according to the invention is explained in more detail belowby way of example and with reference to FIG. 1. FIG. 1 shows a partialcross section through a centrifuge used in the method according to theinvention.

EXAMPLE

The method is basically divided into three method steps. These are:separating the blood plasma particles from the blood plasma suspension(method step I), suctioning off the liquid still present in the drum 4(method step II), and discharging the blood plasma sediment from thedrum 4 and then diverting it into a collecting container 7 locatedunderneath the drum 4 by way of a deflector ring 6 (method step III).

Since blood plasma is very temperature-sensitive, the drum 4 isprecooled before method step I. This is done by feeding a precoolingliquid through the admission line 2, while the drum is rotating, andcooling the jacket of some or all of the structural parts surroundingthe drum, such as housing 1, deflector ring 6 or collecting container 7,and by feeding liquid nitrogen into the space 10 surrounding the drumvia one or more attachments 16 arranged on the housing 1, on thedeflector ring 6 or on the collecting container 7. The drum which hasthus been brought to the desired temperature is then emptied, whilestationary, by suctioning off the precooling liquid through theadmission line 2, in order to avoid contamination of the product by theprecooling liquid. Since precooling liquid may remain between the gapsof the baffle plates 14 because of the capillary effect, the drum 4 isset in rotation during the suctioning or during an interruption in thesuctioning operation, by which means any precooling liquid still locatedbetween the baffle plates 14 is centrifuged out and, after the drum hasbeen stopped, also suctioned off.

During method step I), the blood plasma suspension is fed via theadmission line 2 into the lower area of the drum 4, the incomingsuspension being gently pre-accelerated by rotation of the admissionline 2 together with the drum 4 by means of the drive 21. Above thebaffle plates 14, the clarified solution is taken up by a so-calledscoop 8, which is designed like a pump impeller, and removed via a line3 connected to the latter. To reduce the temperature of the outflowingclarified liquid relative to the temperature of the inflowingsuspension, the clarified liquid can run off through the line 3 free ofpressure.

At the end of method step I), when the collecting space 9 for solidswhich surrounds the baffle plates 14 has been at least partially filledwith solid material a so-called secondary centrifugation phase begins,if necessary, in which the drum 4 is kept rotating, but without any morefresh suspension being delivered, in order in this way, by means of thecentrifugal forces, to compact the blood plasma sediment located in thedrum 4 and thus further reduce the liquid content.

After method step I) or the secondary centrifugation phase, and beforemethod step III), the liquid still present in the drum 4 is suctionedoff via the admission line 2, with the drum 4 stationary, in method stepII). In this way, the blood plasma sediment can be discharged withoutliquid, by which means the solid concentration of the discharged bloodplasma sediment can be substantially increased.

To start method step III), the drum 4 is accelerated, and thedischarging of the blood plasma sediment 18 is started by opening thedischarge slits 5.

The blood plasma sediment 18 which is centrifuged out is deflected bymeans of a so-called deflector ring 6 in the direction of the collectingcontainer 7 underneath it and is taken up either by the collectingcontainer 7 itself or, as in FIG. 1, by a flexible bag 15 which has beenfitted into the collecting container 7. When using a flexible bag 15,the latter is held firm optionally against the inside wall of thecollecting container 7 by means of a vacuum which one or more vacuumattachments 13 generate at the collecting container 7 between the bag 15and the inside wall of the collecting container 7. The flexible bag 15is in this case of such a stable design that it is able to be fittedinto the collecting container 7 before the start of the method and canremain in the collecting container 7 throughout the method andwithstands the shear forces resulting from the air friction from therotation of the drum 4 and also the forces arising upon discharging ofthe blood plasma sediment.

After the blood plasma sediment has been discharged, it is possible,depending on the degree of filling of the collecting container 7 orflexible bag 5, either for a new method cycle to be immediately begunwith method step I) or for the collecting container 7 or the bag 15lying in the collecting container 7 first to be changed, with the drum 4stationary, or if necessary cleaned, before a new cycle is begun withmethod step I).

When changing the collecting container or the bag 15 lying in thecollecting container 7, the discharged blood plasma sediment is ifnecessary cooled before removal, with the drum 4 rotating and withliquid nitrogen 16 being fed in, before it is removed.

Throughout the entire method, or only during individual method steps orintermediate steps, the drum 4 and the product is alternately or jointlycooled by cooling the jacket of some or all of the structural partssurrounding the drum, such as the housing 1, the deflector ring 6 or thecollecting container 7 (jacket 17). The cooling agent (glycol/water;50:50) is introduced via the attachment 19 and removed via theattachment 20. The drum and the sediment is additionally cooled byfeeding liquid nitrogen, through one or more attachments 16 arranged onthe housing 1, on the deflector ring 6 or on the collecting container 7,into the space 10 surrounding the drum, especially into the upper areaand lower area of the space 10 surrounding the drum. Nitrogen gas isremoved again via an exhaust gas pipe 11.

During individual chosen method steps, the surface temperature of thedrum 4 is measured by a temperature-measuring device 12 which isarranged on the housing 1 and conducts contactless measurement. This hasthe particular advantage that, by adjusting the centrifuge cooling, thesurface temperature of the drum 4 can be adapted to the intaketemperature of the blood plasma suspension, and it is thus possible toavoid heat being conducted from outside into the drum with consequentheating of the blood plasma sediment separated in the drum.

Example 1

With the described method, it was possible for 22.6 kg of a blood plasmaprotein to be separated and discharged fully automatically from the drumin 5 cycles within 70 minutes. About 30% of this time was taken up bythe separation of the blood plasma particles in method step I. Betweenmethod steps I and II, a secondary centrifuging phase of 5 minutes wasperformed in order to further compact the blood plasma sedimentseparated in the drum.

The drum speed during separation of the blood plasma particles (methodstep I) was 7000 l/min. Before the start of method step I, the drum 4was precooled by feeding in a water/ethanol mixture as precooling liquidwith a temperature in the range of −5° C. to −10° C. This precooling wasassisted by cooling the jacket of the housing 1 (−10° C.), of thedeflector ring 6 (−20° C.) and of the collecting containers 7 (−20° C.)and by feeding in liquid nitrogen at housing 1 and deflector ring 6.This cooling was also maintained for subsequent method steps II and III.During the precooling phase, the drum speed was first set at 4000 l/minand, after a drum temperature of about −4° C. had been reached, was setat 7000 l/min. In this way it was possible to reach a drum temperatureof 4 to −6° C. measured by a contactless temperature-measuring device12.

The temperature of the blood plasma suspension fed in through theadmission line 2 during method step I was ca. −5° C. By means of thepressure-free removal of the clarified blood plasma liquid via theremoval line 3, it was possible to limit the heating of the liquid,relative to the intake temperature, to only about 1.0° C. After thefinal method cycle, the discharged blood plasma sediment was cooled in a5-minute cooling phase at a drum speed of 1000 l/min and withintroduction of liquid nitrogen into the space 10 surrounding the drum4. The discharged blood plasma sediment thereafter had a temperature of−5° C. to −6° C.

Example 2

In another example, another blood plasma fraction was separated off. Inthis case, it was possible for 16.3 kg of blood plasma sediment to beseparated off and removed fully automatically in 4 cycles within 81minutes. Ca. 22% of the time was taken up by the separation of the bloodplasma particles in method step I. Between method steps I and II, asecondary centrifuging phase of in each case 15 minutes was performed inorder to compact the blood plasma sediment separated off in the drum.

The drum speed during separation of the blood plasma particles was 7000l/min in this case too. Before the start of method step I, the drum 4was precooled by feeding in a water/ethanol mixture as precooling liquidvia the admission line 2 with a temperature in the range of −10° C. to−13° C. The jacket cooling of the structural parts surrounding the drum4, namely housing 1, deflector ring 6 and collecting container 7, was inthe range of −17° C. to −23° C. The cooling was once again assisted byfeeding in liquid nitrogen at housing 1 and deflector ring 6 (attachment16). This cooling was also maintained for subsequent method steps II andIII. In the precooling phase, the drum speed was raised in stages froman initial 4000 l/min to 7000 l/min here as well.

During the precooling phase, the drum speed was first set at 4000 l/minand, after a drum temperature of about −5° C. had been reached, was setto 7000 l/min. In this way it was possible to reach and to maintain adrum temperature of −1° C. to −7° C. The temperature of the blood plasmasuspension fed in through the admission line 2 during method step I was−6° C. to −7° C. Here once again, the clarified liquid was removed freeof pressure via the removal line 3. The heating of the liquid relativeto the intake temperature was in this case <1° C. In this test, nofurther cooling phase at low drum speed was needed to reach the desiredtemperature of the discharged blood plasma. The discharged blood plasmasediment had a temperature of −5° C. to −6° C.

1. A method for the separation of blood plasma particles from a bloodplasma suspension in a self-discharging centrifuge, having at least ahousing (1) that is optionally coolable, an admission line (2) for thesuspension, a removal line (3) for the clarified liquid, a drum (4),which is suspended and is connected to a drive part lying above it, and,is provided with two or more discharge slits (5) and axially stackedbaffle plates (14), and a collecting container (7) that is optionallycoolable, the method comprising at least the following method steps (I)separating the solid blood plasma particles from the liquid phase, as asediment, by centrifuging the blood plasma suspension and removal of theliquid phase, (II) suctioning off the liquid still present in the drum(4) after separation of the blood plasma particles, the drum optionallybeing brought to a stop at least for at least 5 seconds, (III)discharging the sediment of solid blood plasma particles from the drum(4), by centrifugal force and opening of the drum (4), into a collectingcontainer (7) located underneath the drum (4) wherein during one or moreof steps (I) to (III) the drum and the blood plasma sediment are cooled.2. The method as claimed in claim 1, wherein the temperature of the drum(4) is brought to a temperature of ±5° C. in relation to the temperatureof the inflowing blood plasma suspension before step I.
 3. The method asclaimed in claim 2, wherein said temperature adjustment of the drum (4)before method step I) is made with the drum (4) rotating.
 4. The methodas claimed in claim 2, wherein said temperature adjustment of the drum(4) before method step I) is made by feeding a precooling liquid via theadmission line (2).
 5. The method as claimed in claim 4, wherein, aftersaid temperature adjustment of the drum (4) before method step I), theprecooling liquid is auctioned off from the drum (4) via the admissionline (2).
 6. The method as claimed in claim 2, wherein, during methodstep I), the liquid phase separated in the drum (4) is taken up by ascoop (8) positioned above the baffle plates and is removed via aremoval line (3).
 7. The method as claimed in claim 1, wherein, betweenmethod steps I) and II), in an additional centrifuging phase, the bloodplasma sediment is further compacted at a drum speed of80% to 130% ofthe separation speed in step I).
 8. The method as claimed in claim 1,wherein step (II) comprises one or more spinning steps.
 9. The method asclaimed in claim 1, wherein, in method step III), the blood plasmasediment is discharged by opening the discharge slits (5) of the drum,at a drum speed of 30% to 130% of the separation speed in step I). 10.The method of claim 9, where said discharge slits are opened at a drumspeed which is equal to the drum speed of step (I).
 11. The method asclaimed in claim 1 wherein the blood plasma sediment discharged from thedrum (4) is collected in a flexible bag (15) which is fitted into thecollecting container (7) and which is held against the inner wall of thecollecting container (7) by a vacuum which is generated by a vacuumattachment (13) between the bag (15) and the inner wall of thecollecting container (7).
 12. The method as claimed in claim 1, wherein,after method step III), the method steps I) to III) are immediatelyrepeated, until the collecting container (7) is filled with blood plasmasediment to a predetermined degree, and the sediment is removed forfurther processing.
 13. The method as claimed in any one of claims 1through 12, wherein the drum (4) and the discharged blood plasmasediment are cooled, independently of one another, by cooling a jacketon those parts of the centrifuge surrounding them, parts of the housing(1) and/or of the collecting container (7) with a liquid cooling medium,in the temperature range of +2° C. to −50° C.
 14. The method of claim13, wherein said parts which are cooled are the housing, or thecollecting container, or both.
 15. The method as claimed in any one ofclaims 1 through 12, wherein during the entire method, or duringselected steps thereof, at least before removal of the sediment the drumand the sediment is cooled by feeding liquid nitrogen into a space (10)surrounding the drum (4), and the gaseous nitrogen is removed via anexhaust gas pipe (11) preferably positioned in the housing.
 16. Themethod as claimed in claim 1, wherein, during the method, the surfacetemperature of the drum (4) is checked at one or more locations by atemperature-measuring device (12) which is optionally arranged on thehousing (1) and conducts contactless measurement.
 17. The method ofclaim 1, wherein said drum is brought to a stop for at least 10 secondsin step (II).